When a position detection device is used to detect an operating position of a piston of a hydraulic pressure cylinder and the detected signals are used as various control signals, the position detection device is mounted on the hydraulic pressure cylinder. The position detection device is configured to detect magnetism of a permanent magnet which is mounted on the piston by using a magnetic sensitive type position sensor which is mounted on the outer surface of the cylinder tube. Various mechanisms have been used to mount the position sensor on the outer surface of the cylinder tube.
FIGS. 12 and 13 show an example of a known hydraulic pressure cylinder 30 on which a position sensor 21 is secured, and a position sensor attachment band used for securing the position sensor 21. The hydraulic pressure cylinder includes a cylinder tube 31 formed in a cylindrical shape having a cylindrical hole inside thereof, a piston housed in the cylinder tube 31 so as to be slidably movable along a center axial line L, and a piston rod 33 which is connected to the piston and extends to the outside of the cylinder tube 31. The piston moves forward and backward by alternately supplying and exhausting a pressure fluid (for example, compressed air) to and from pressure chambers which are disposed on each end of the piston through a port 36a on a rod cover 34 disposed on one end of the cylinder tube 31 and a port 36b on a head section 35 disposed on the other end of the cylinder tube 31. Further, a ring-shaped permanent magnet is mounted on the outer periphery of the piston such that the position sensor 21 detects the magnetism of the permanent magnet and output the detected signals of the operating position of the piston.
In the hydraulic pressure cylinder 30, a position sensor attachment band 10A that is used to place a holding member 20 that holds the position sensor 21 at a certain position on the outer periphery of the cylinder tube 31 generally includes a pair of opposed clamp members 11(a), 11(b) on both ends of a thin plate band 13 which is wound around the outer periphery of the cylinder tube 31 so as to clamp the holding member 20 from both sides with the holding member 20 holding the position sensor 21. The position sensor holding member 20 is clamped by the clamp members 11(a), 11(b) and is secured by screwing a mount screw 14.
The position sensor attachment band 10A in FIG. 12 is configured to allow the mounting position of the position sensor 21 to be flexibly adjustable by moving the position sensor 21 on the cylinder tube 31, and needs to have a sufficient securing force to prevent the position sensor 21 from being displaced when a force of a certain magnitude is inadvertently applied on the position sensor attachment band 10A by an operator. The securing force of the position sensor attachment band 10A is a maximum resistance of the position sensor attachment band 10A in a secured state to a force in the circumferential direction and the axial direction of the cylinder tube 31 which is applied on the position sensor attachment band 10A.
When the clamp members 11(a), 11(b) are fastened by the mount screw 14 to generate the securing force on the position sensor attachment band 10A, a tension is generated on the thin plate band 13, which generates a pressure distributed over the entire contact surface of the thin plate band 13 and the cylinder tube 31. This pressure distribution allows the securing force to be generated on the position sensor attachment band 10A. However, this securing force does not always exceed the magnitude of securing force required for the device, since the securing force is distributed over the entire contact surface of the thin plate band 13 and the cylinder tube 31. Further, the securing force of the position sensor attachment band 10A is subject to the effect of a state change such as inclination of the position sensor attachment band 10A during mounting and torsion of the position sensor attachment band 10A during tightening of the mount screw 14, which causes the securing force to be unstable.
In order to increase the securing force, providing a rubber lining on the thin plate band is known as disclosed in Patent Literature 1. When a lining made of a material such as a rubber having a high friction resistance is applied on the inner peripheral surface of the thin plate band, instability of the position sensor attachment band 10A is eliminated, thereby obtaining a high securing force. However, there are problems that it is difficult to ensure that a rubber having a uniform thickness is applied on the thin plate band, and the manufacturing cost is increased. Further, when the thin plate band is secured at the same position for a long period of time, a rubber is stuck on the cylinder tube 31, which causes a position adjustment of the position sensor attachment band 10A to be difficult.
Further, in the position sensor attachment band 10A on which the lining is applied, there is a problem that the securing state of the holding member that holds the position sensor is subject to the effect of the thickness of the lining. If the thickness of the lining is decreased, there is a risk that securing of the position sensor 21 is not stabilized due to reasons such as a gap being formed between the cylinder tube 31 and the bottom of the holding member of the position sensor 21 when the position sensor attachment band 10A is mounted on the cylinder tube 31. On the other hand, when the thickness of the lining is increased, mounting of the mount screw may be difficult, or in an extreme case, mounting of the mount screw may be impossible when the position sensor attachment band 10A is mounted on the cylinder tube 31. Accordingly, the manufacturing cost of the position sensor attachment band 10A is increased since a high accuracy is required for the thickness of the lining member and the like. Further, in the mounting structure of the position sensor in Patent Literature 1, a plurality of components such as a strip band and anti slipping rubber plate are necessary, and the increased number of components leads to increase in manufacturing cost.